Modern wireless communications systems typically employ separate time and/or frequency resources for downlinks (DL) and uplinks (UL). For example, in frequency division modulation (FDM), downlinks employ radio-frequency (RF) carriers over frequency range(s) that are different from the frequency ranges of RF carriers used for the uplinks. In time division multiplexing, such as time division duplexing (TDD), the DL and UL employ different time resources, such that uplink communications take place at different time slots or frames than downlink communications. Because of the practice of employing TDD or FDM in wireless communications, the full time/frequency capacity for conduction of wireless communications has not yet been exploited.
In order to exploit the ability to conduct simultaneous transmission (Tx) and reception (Rx) (STR) over the same frequency and time range, it may be desirable to improve present day apparatus and procedures for conducting duplex communications. For example, when Tx and Rx signals use the same RF carrier and time slot, a high power Tx signal typically leaks to the receive chain through a duplexer as an echo. The term “echo” is used to refer to an undesired feed-through of a transmitted data signal into a receiver.
In many circumstances, this high power echo may create a severe interference to what may be a very weak signal, such as a signal received from a cell edge of a radio access network. Due to impedance mismatching at an antenna and cable, echoes can appear at the receive chain. In addition, a transmitted signal can be reflected in the air and may return to a system as multiple echoes that can interfere with the weak desired receive signal. As an example, a Tx signal may be transmitted at 46 dBm. A typical duplexer may exhibit 20˜40 dB leakage. Accordingly, even assuming 40 dB leakage at the duplexer, a 6 dBm echo can result to contaminate the desired (weak) receive signal. Without cancelling such STR interference caused by echoes, the intended received signal may not be decoded because the signal strength of the echo swamps the intended received signal.
It is with respect to these and other considerations that the present improvements have been needed.